Gerald C. Quintana, Senior .NET / Full-Stack Engineer

Building reliable business applications, APIs, and AI-powered solutions in .NET.

I design and build the systems businesses run on: client portals, internal tools, APIs and the SQL Server databases behind them.

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Experience: 10 years
Core stack: C#, ASP.NET Core, SQL Server
Based in: Bulacan, Philippines

About me

I have spent 10 years building enterprise and client-facing web applications, APIs and business systems, mostly in C# and ASP.NET. My work has covered government portals, payment and revenue collection, HR systems, and the internal tools and client portals that small and mid-sized businesses depend on every day.

I work across the full stack. On the back end that means ASP.NET Core, Web API, Entity Framework and SQL Server. On the front end it means Razor, JavaScript and Bootstrap interfaces that the people using them can learn quickly.

More recently I have been adding OpenAI API features to the systems I build, where they save people real work. AI is one more tool in how I build business software, not a replacement for sound engineering.

Technical skills

The tools I use in production work.

Back end

Data

Front end

APIs and integrations

Tools and delivery

Featured projects

Client and private projects are labeled. Where a system is not public, I describe it in a case study instead of linking to it.

Pool Safety Network client portal

Client project

A client portal for an Australian pool and spa compliance business, used to manage jobs, RFIs, documents, activities and workflows.

Problem solved: Pool, spa and outdoor building projects move through permit and compliance steps with many documents and follow-up questions. The business needed one place for customers and staff to track each job from first enquiry onward.
My role: Full-stack developer
Technologies: ASP.NET Core
C#
Razor Pages
SQL Server
Azure Blob Storage
OpenAI API
Image processing
Bootstrap 5
AES encryption
Key features: Public project intake that scopes the job and permit pathway
Job, RFI and activity tracking
Document upload and management on Azure Blob Storage
Workflow steps for compliance tracking
Encrypted URL parameters for secure links
OpenAI API and image processing features

Sola Dental Tools

Client project

An internal business application for a multi-location dental group, covering patient surveys, SMS communications, user management, audit records and reporting.

Problem solved: Staff across several offices needed one secure place for patient surveys, patient text messaging and the reports leadership relies on, instead of separate tools and manual exports.
My role: Full-stack developer
Technologies: C#
ASP.NET Core
SQL Server
JavaScript
Twilio
Google Sheets
Power BI
Key features: Patient survey management
SMS communications through Twilio
User management and sign-in
Audit records
Reporting workflows with Google Sheets and Power BI integrations
A central hub linking staff to dashboards and approved third-party tools

Earlier work

Government online portal
Private / Client Project
A web portal for a government office covering vehicle registration, license processing and secure authentication.
C#, .NET Core, ASP.NET MVC, REST API, SQL Server
Online revenue collection system
Private / Client Project
A secure payment processing system for government transactions, with real-time reporting and audit trails.
C#, .NET Core, ASP.NET MVC, REST API, SQL Server
HRIS and employee self-service
Private / Client Project
A human resources information system with employee self-service on web and mobile, integrated with SAP modules.
C#, ASP.NET MVC, REST API, SQL Server, SAP integration
Real estate listing platform with AI content
Private / Client Project
A property listing platform with Google Maps integration and the ChatGPT API for drafting property descriptions and sales pitches.
C#, ASP.NET MVC, REST API, SQL Server, ChatGPT API, Google Maps
Personal portfolio
Public project
My earlier portfolio site, hosted on GitHub Pages.
HTML, CSS, JavaScript, GitHub Pages
- View project (opens in a new tab)

Professional experience

10 years
Senior .NET / Full-Stack Engineer
Enterprise and client-facing web applications, APIs and business systems for government agencies, global clients and private enterprises.
- Built government web portals for vehicle registration and license processing, and a revenue collection system with reporting and audit trails.
- Developed an HRIS and employee self-service system for web and mobile, integrated with SAP modules.
- Built a client portal for a pool and spa compliance business in Australia, covering jobs, RFIs, documents and workflows.
- Built internal business tools for a multi-location dental group: patient surveys, SMS, user management, audit records and reporting.
- Integrated the OpenAI API into production business applications.

What I can build

The kinds of systems I am hired for.

Client and customer portals
Sign-in, role-based access, document upload and storage, and the job or case workflows your clients follow.
ASP.NET Core, Razor Pages, SQL Server, Azure Blob Storage
Internal business tools
Admin screens, user management, audit records and the day-to-day tools that replace spreadsheets and manual steps.
ASP.NET Core, ASP.NET MVC, Entity Framework, Bootstrap
REST APIs and system integrations
APIs that other systems can depend on, and integrations with SMS, payment, mapping, ERP and reporting platforms.
Web API, REST, Twilio, SAP
Reporting and data flows
Getting operational data out of the application and into the reports and dashboards people actually read.
SQL Server, Google Sheets
Maintaining existing .NET systems
Extending and stabilizing established ASP.NET MVC and .NET applications without disrupting the people who rely on them.
ASP.NET MVC, .NET, SQL Server, Azure DevOps

AI and API integrations

I add AI features to business applications where they remove repetitive work. They sit inside a normal .NET system, with the same data, permissions and logging as everything else.

Where I have used it

Generated listing content. A real estate platform used the ChatGPT API to draft property descriptions and sales pitches for agents to review.
AI inside a client portal. The Pool Safety Network portal calls the OpenAI API alongside image processing and Azure Blob Storage for project documents.

How I build it

API keys stay on the server. The browser never talks to the model provider directly.
AI output that reaches customers is reviewed or validated first.
The feature has to justify its cost and latency against a plain, deterministic solution.

Other APIs I have integrated: Twilio SMS, Google Sheets, Power BI, Google Maps, Radar API, SAP.

Contact

Open to senior .NET and full-stack roles, and to contract work on business systems.

Email: giequintana@gmail.com
LinkedIn: linkedin.com/in/gerald-quintana-6a9134a2
GitHub: github.com/giequintana

Resume / CV

A one-file PDF with my full work history.

Download resume

Building reliable business applications, APIs, and AI-powered solutions in .NET.

Back end

Data

Front end

APIs and integrations

Tools and delivery

Pool Safety Network client portal

Sola Dental Tools

Earlier work

Government online portal

Online revenue collection system

HRIS and employee self-service

Real estate listing platform with AI content

Personal portfolio

Senior .NET / Full-Stack Engineer

Client and customer portals

Internal business tools

REST APIs and system integrations

Reporting and data flows

Maintaining existing .NET systems

Where I have used it

How I build it

Resume / CV

Building reliable business applications, APIs, and AI-powered solutions in .NET.

Back end

Data

Front end

APIs and integrations

Tools and delivery

Pool Safety Network client portal

Sola Dental Tools

Earlier work

Government online portal

Online revenue collection system

HRIS and employee self-service

Real estate listing platform with AI content

Personal portfolio

Senior .NET / Full-Stack Engineer

Client and customer portals

Internal business tools

REST APIs and system integrations

Reporting and data flows

Maintaining existing .NET systems

Where I have used it

How I build it

Resume / CV